Combined fuse and demand meter



SePt- 29, 1953 H. w. MERTENS COMBINED FUSE AND DEMAND METER Filed Nov. l, 1947 2 Sheets-Sheet l Sept. 29, f1953 H. w. MERTENS COMBINED FUSE AND DEMAND METER 2 Sheets-Shea?l 2 Filed Nov. l, 1947 jfff/v M /yer/L?? BY ZE Patented Sept. 29, 1953 COBIBINED FUSE AND DEMAND METER Henry W. Mertens, Auburn, Maine, assigner to McGraw Electric Uom'pany, a corporation ot Delaware Application November 1, 19.47., Serial No. 783,578

1 Claim. l

In .distribution systems it is 'desirable to know the load being carried by a transformer, particularly the .maximum load. 'Heretofore it was necessary to open Athe line and insert what is known as ya demand meter 'in the circuit as a temporary installation. This caused interruption of the service. Another method that has been followed was to employ a so-called :clip-on ammeter which usually .had a split core transformer which could be opened up and hooked around the line conductor. 'This transformer had a secondary connected to a meter to indicate the maximum current ilowing. Neither of these methods were wholly lsatisfactory and each required a considerable amount of work to make the temporary installation and to vlater remove it.

This invention is designed to provide a means of utilizing a portion of the fuse structure which is almost always found on the primary side of the transformer so that it is not necessary to open the line and disrupt the service or to do any material amount of Work but which merely .requires the operator to substantially instantly substitute a combined fuse and demand meter for the conventional fuse and thus maintain the protection afforded by the fuse and at the same time have a demand meter in the line to register the peak load on the transformer.

In greater detail, further objects are to provide a fuse door assembly for a housed fuse construction in which a demand meter is carried by the door on its outer side and connected in series with a fuse link located Within a fuse tube carried on the inner side of the door and arranged so that the fuse tube, demand meter and door assembly can be substantially instantly substituted for the conventional fuse tube and door assembly.

An embodiment of the invention is shown in the accompanying drawings, in which:

Figure 1 is a vertical sectional view through the device.

Figure 2 is a fragmentary view of the lower portion thereof with the cover and intermediate partition of the demand meter removed.

Figure 3 is a fragmentary face view of the lower portion of the device showing the demand meter as it normally appears.

Referring the drawings, it will be seen that the device comprises a porcelain or other insulating housing I provided with an insulating door 2 which may have a manipulating handle or eyelet portion 3. The door 2 is provided with trunnions 4 which t within hook-like brackets 5 so that the door may be freely removed in the usual man- (Cl. 32k-103) ner. The housing I 1s provided with 'an upper terminal 6 and a 'lower 'terminal I adapted to 'receive the line and load wires, respectively. A fuse tube y8 is carried by the door and is provided with an upper contact "9 and an intermediate contact ID, respectively, normally engaged with 'the upper and lower stationary terminals '6 and 1. A fuse link indicated generally at I I extends through the fuse tube .and out through its .open bottom end 'and its lower end is clamped "in place by means of the thumb screw I2 carried by a threaded stud I3 on the bottom contact IB of the fuse tube. The bottom 'contact I '4 may be provided with a vnip-out lever or throw-out lever I5 which 'is spring urged downwardly and arranged to extract any remaining portion of the fuse link on rupture thereof.

Itis to be noted that the lower contact I4 of the fuse tube 8 is not directly electrically connected to the intermediate contact III of the fuse tube. lInstead a conductor 'I6 leads 'from the lower -contact I4 to a demand meter indicated generally lby the reference character Il and the return conductor from the demand meter indicated at I8 leads to the intermediate contact ID of the fuse tube. It will be seen, therefor, that the current passes from the upper stationary terminal 6 through the fuse link to the lower contact I4 of the fuse tube. From this point current passes through the demand meter and back to the intermediate contact Il) of the fuse tube and from there to the stationary terminal 1. The conductors I6 and I8 are connected to opposite ends of a bi-metal strip I9 anchored at its upper end as indicated at 20 and free at its lower end. The conductor I8 is necessarily made flexible to accommodate the slight motion of the bi-metal member I9 when it is heated by the current.

The free end of the bi-metal strip I9 is pivoted to a transversely extending insulating link 2|. The other end of the insulating link 2| is pivoted to the free end of a second bi-metal member 22 which does not carry any current but corrects for the ambient temperature. The bi-metal member 22 is rigidly carried at its upper end by means of a pivotally mounted hub 23. The hub also rigidly carries a light, elongated nger 24 which has an outwardly projecting end 25. The finger or end 25 passes through an opening 26 in the intermediate partition 21 and in the scale plate 28. 'I'he scale plate or insignia bearing plate 28, see Figure 3, is provided with a scale and graduations indicated generally by the reference character '28 to show the amount of current passing. A pointer 30 is pivoted on the pin 3| and is provided with and is so arranged that it tends to rotate the hub 23 a slight amount so as to move thei'lnger 25 to the right, as viewed in Figures 2 and 3, an amount suiiicient to correct for ambient temperature.

It is to be distinctly understood that the housing I with its stationary terminals is a conventional fuse housing and normally receives a door rand fuse assembly. When it is desired to employ The casing 35 of the demand meter is provided with a transparent front plate 36 to allow a View of the scale and pointer and to protect the parts of the demand meter from the weather. The only opening into the demand meter is the slot 34 and this is located in its bottom wall.

Although this invention has been described in considerable detail it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

I claim:

In a device of the class described, a housing having an upper and a lower stationary contact, said housing having means for removably receiving doors provided with fuses, a door arranged to v be received by said housing, a fuse structure the demand meter to indicate the maximum load on a transformer, for instance, all that is necessary is for the lineman to remove the conventional door from the housing l and substitute the door, fuse tube and demand meter assembly hereinabove described. This change can be made substantially instantaneously with only a very brief interruption of the service. Also it is to be noted that the circuit does not have to be opened up in order to place the demand meter in the circuit, as all that is necessary is merely to substitute the door, fuse tube and demand meter assembly for .the conventional door and fuse tube assembly. Obviously the maximum load in amperes will be indicated by the demand meter and the lineman can thereby ascertain the exact load carried by the transformer or other device with Which the demand meter is in series. It is to be noted also that the insulating pointer Si! is provided with a rounded portion 33 which projects through a slot 34 formed in the casing 35 of the demand meter. This rounded portion can be engaged by the thumb of the operator or lineman and the demand meter can, therefore, be reset. It is preferable to make the pointer 3i) with its rounded portion 33 of insulating material.

carried on the inner side of said door and including a `fuse tube having three distinct and separate contacts including an upper, a lower, and an intermediate contact with the upper and intermediate contacts arranged to respectively engage the upper and lower stationary contacts of said housing'when said door is in closed position, a fuse link within said tube electrically connecting the upper and lower contacts of said fuse tube, and a meter connected between the intermediate and lower contacts of said fuse tube.

HENRY W. MERTENS.

References Cited in the le of this patent UNITED STATES PATENTSv Number Name Date 891,561 McGowan et al. June 23, 1908 1,194,883 Sachs Aug. 15, 1916 1,269,770 Wurdack June 18, 1918 2,385,473 Schultz Sept. 25, 1945 2,452,872 Schultz Nov. 2, 1948 FOREIGN PATENTS Number Country Y Date 285,806 Great Britain Aug. 2, 1928V 394,814 Great Britain July 6, 1933 

